Composite tube



Sept. 17, 1935. A HARNSBERGER 2,014,564

COMPOSITE TUBE Filed May 9, 1930 J w k' AudkjE. arnsber er Patented Sept. 17, 1935 rrso s'r COMPOSITE TUBE Audley E. Harnsberger, Chicago, 111., assignor to The Pure Oil Company, Chicago, 111., a corporation of Ohio Application May 9, 1930, Serial No. 451,022

6 Claims.

This invention relates to improvements in tubular fluid heaters and has particular reference to heaters wherein fluids are passed in confined streams through externally heated tubes.

In certain types of heaters of this kind the tubes are disposed in furnaces having refractory walls and wherein certain portions of the fluid conducting tubes are subjected to a high degree of externally applied heat while other portions of the tubing are disposed in furnace zones wherein lower temperatures prevail thereon. Thus it is a common practice to position a single fluid conducting tube in the radiant heat zone of a furnace wherein the rate of heat input into the tube and the fluids passing therethrough is high and to position other portions of the same tube in the convection heat zone of the furnace wherein the rate of heat input is lower and a marked difference exists in the furnace temperatures surrounding the tube.

It has been found that in a heater of this character that portion of a fluid heating tube disposed in the radiant or high temperature heat zone deteriorates rapidly due to the high temperatures or oxidation influences on the tube set up thereby whereas that portion of the tube in the low temperature zone lasts indefinitely and is not deleteriously affected by the furnace temperatures un der operating conditions.

It is, therefore, an object of the present invention to provide an improved tube construction for fluid heaters wherein that portion of the tube which is situated in the high temperature or radiant heat zone of the furnace is formed from an alloy which resists oxidation and high tempera ture conditions but which is comparatively expensive to produce and wherein the length or lengths of the tube disposed in the lower temperature zones of a furnace is formed from ordinary metals and which are of less expensive construction than those used in the high temperature zone, whereby a composite tube is produced which possesses a long operating life in a furnace and also one which may be produced at the lowest possible cost commensurate with the longevity of the tube.

It is another object of the invention to produce a composite tube of the character specified wherein that portion of the tube whichis disposed in the high temperature zone of a furnace is formed from a chrome alloy metal and which is welded to the adjoining end of that section of the tube formed from less costly materials and wherein the composite welded tube will possess all necessary mechanical strength together with improved re sistance to the metal destroying temperatures which prevail in furnaces or heaters of the type in which tubes of this character are employed.

For a further understanding of the invention reference to be had to the following description and the accompanying drawing wherein: 5

Figure l is a vertical sectional view taken through a heater provided with tubes formed in accordance with the present invention, and

Figure 2 is a detail longitudinal sectional view taken through the composite tube at the welded 10 joint existing between the two sections thereof composed of different metals.

In the accompaniyng drawing has been illustrated a heater of the type commonly used in the heating of liquid and vaporized oils, either for the 15 distillation or cracking of such oils and vapors.

It will be understood as the description proceeds that the invention is not limited to a heater of the specific type disclosed, but may be used in connection with the heating of other fluids and for other 20 purposes, and I contemplate herein all such uses to which my invention may be placed. The heater, indicated generally by the numeral i, however, clearly sets forth the features of the present invention and for this reason the folio-wing de-- 25 scription will be specifically directed thereto.

The heater I embodies a wall structure 2 which is provided interiorly with a transversely extending bridge wall 3, which divides the interior of the wall structure into radiant and convection 30 heat zones 4 and 5 respectively. Arranged in the zone 4 is a burner mechanism ii by which any desired furnace temperature may be maintained in said heater, depending upon the particular operation which is carried out therein. In the 35 simple distillation of oils, for example, the furnace temperature is considerably lower than that which is used in similar furnaces or heaters wherein oil is subjected to cracking or conversion operations, and likewise when fluids other than oils or oil vapors are to be heated these temperatures may vary.

In the heater illustrated there is provided in the upper portion of the setting or wall structure a horizontal row of tubes '1 which are supported by the front wall 8 of the setting, the rear wall 9 and preferably rests at their intermediate portions on the upper part it of the bridge wall 3. Each of the tubes 7 is of composite construction. That is to say, that length of each tube 50 l which passes through the high temperature or radiant heat zone l of the heater is formed from a chrome alloy. These alloys may consist, for example, of 18% chromium, 8% nickel and the remainder iron, up to alloys containing 28% chromium, with a low nickel content and the remainder substantially iron. At present, these alloys are quite expensive and this factor tends to minimize their use in heater constructions. The chromium containing section of each of the tubes 1 is indicated by the numeral I i and, as shown, passes through the radiant or high temperature heat zone s of the furnace. The other continuing section of the tube 1, which is indicated by the numeral [2, is preferably formed from steel which may or may not be calorized to increase its resistance to oxidation. It will, therefore, be understood that either plain steel, calorized or other less expensive metals suitable for present purposes may be used in the convection heat zone 5 of the heater, or in the lower temperature zones thereof.

To secure the sections H and it! together the abutting ends 53 of said sections are chamfered or beveled as at M to produce an annular V- shaped ecess. During the process of welding the adjoining ends are held together by, for example, the employment of an inside expanding mandrel (not shown) positioned within the tub ing. I then lay on a bead by the employment of a high test wire, known as Oxweld No. 1, and follow this operation with a special high chrome wire for finishing the weld, the completed weld being indicated by the numeral l5. Any surplus welding material is then ground off in order that the outside diameter of the tubing at the point of the weld will not exceed the general outside diameter of the tubing. This is done in order that the entire tube may pass through a return bend without difficulty. The welded joint l5 may or may not be protected by the employment of refractory material when the tubing is positioned for operation in a furnace, depending on local temperature conditions. Generally, however, these welds are placed in such location in a furnace that the radiant or other heat applied thereto is modified to a point where oxidation of the weld will not result. In the present heater, the welded joint is shown as being located over the bridge wall 3 and spaced from the high temperature chamber 4 of the furnace. The fluid entrance ends of each of the tubes l are provided with collars l6 located outside of the furnace. These collars are provided on account of the difficulty of rolling some of the high chrome tubes of the character specified into a return bend or header, due to brittleness, or high co-efiicient of expansion. By the employment of the collars l6, which usually are of ordinary steel, facility is to be obtained in the matter of connecting the fluid inlet ends of the tube with the oil vapor inlet header ll. The discharge end f the steel section E2 of each of the tubes 7 is connected with a return bend E8 to which is connected a second pass of ordinary steel tubes I9 which may or may not be calorized or otherwise treated to resist oxidation. The pass of tubes i9 is connected by return bends disposed in the wall 3, with a lower pass of tubes 2! similar in construction and design to the tubes Re. Any desired number of these tube passes may be provided in the convection zone 5, depending upon the fluids being treated.

In View of the foregoing it will be seen that the present invention provides a composite tube for use in high temperature furnaces or heaters and wherein the tube is of such construction that it will resist the deleterious action of high temperature furnace gases. That portion of the tubing which is subjected to high temperatures and radiant heat is made from a. relatively expensive alloy which is capable of resisting the metal destroying action of the prevailing high temperatures, radiant heat and furnace gases in that portion of the furnace wherein such expensive materials are used and, also, that portion of the tubing disposed in the furnace wherein milder operating conditions prevail is formed from a less costly material but one which is fully capable of withstanding without destruction the operating conditions in said zones of milder temperature. By use of the tubing described, I obtain economy in the construction and operation of the furnace, together with long tube life, heating efiiciency and durability.

What is claimed is 1. In an oil heater, a furnace chamber including a high temperature zone and a Zone of lower temperature, a wall separating said zone, a composite oil heating tube passing through said zones,

said tube being composed of a pair of longitudinally aligned welded sections, the section of the tube arranged in the high temperature zone and through which cooler products pass being composed from a steel highly resistant to deterioration and the influence of high temperatures while the other section of said tube through which hotter products pass occupying the zone of lower temperature is composed of ordinary steel, and the welded joint between said sections being supported and protected by said zone separating wall.

2. A heater for cracking hydrocarbon oils which comprises a combustion chamber and a heating chamber with a bridge wall therebetween, heating tubes in said heating chamber, a second group of heating tubes, above said combustion chamber, welded to said chamber tubes and exposed to high temperature radiant heat, said second group being composed of an alloy highly resistant to oxidation at high temperatures and said heating chamber tubes being composed of metal less resistant to oxidation at high temperatures, the welds being protected against exposure to oxidation of the high temperature radiant heat.

3. A heater according to claim 2 in which the heating chamber tubes are composed of plain or calorized steel and the second group of tubes is composed of chrome-nickel steel.

4. A heater in accordance with claim 2 in which the welds are located between the heating and combustion chambers and are protected by refractory material.

5. A heater for cracking hydrocarbon oils which comprises a combustion chamber, a heating chamber, a hollow, upwardly extending bridge wall between said chambers, heating tubes in said heating chamber connected by return bends located in the hollow spaces of the bridge wall and outside the rear wall of the heating chamber, a second group of heating tubes above said combustion chamber exposed to high temperature radiant heat, said second group being composed of an alloy highly resistant to high temperature oxidation and said heating chamber tubes being composed of metal less resistant to high temperature oxidation, said second group and said heating chamber tubes being welded together at a point immediately above the bridge wall, the Welds being supported by said bridge wall.

6. A heater in accordance with claim 5 in which the heating chamber tubes are composed of plain or calorized steel and the second group of tubes is composed of chrome-nickel steel.

AUDLEY E. HARNSBERGER. 

